The use of a hand operated pointing device for use with a computer and its display has become almost universal. By far the most popular of the various devices is the conventional (mechanical) mouse. A conventional mouse typically has a bottom surface carrying three or more downward projecting pads of a low friction material that raise the bottom surface a short distance above the work surface of a cooperating mouse pad. Centrally located within the bottom surface of the mouse is a hole through which a portion of the underside of a rubber-surfaced steel ball (hereinafter called simply a rubber ball) extends; in operation gravity pulls the ball downward and against the top surface of the mouse pad. The mouse pad is typically a closed cell foam rubber pad covered with a suitable fabric. The low friction pads slide easily over the fabric, but the rubber ball does not skid, but instead rolls as the mouse is moved. Interior to the mouse are rollers, or wheel, that contact the ball at its equator (the great circle parallel to the bottom surface of the mouse) and convert its rotation into electrical signals. The external housing of the mouse is shaped such that when it is covered by the user's hand it appears to have a "front-to-back" axis (along the user's forearm) and an orthogonal "left-to-right" axis. The interior wheels that contact the ball's equator are arranged so that one wheel responds only to rolling of the ball that results from a motion component of the mouse that is along the front-to-back axis, and also so that the other wheel responds only to rolling produced by a motion component along the left-to-right axis. The resulting rotations of the wheels or contact rollers produce electrical signals representing these motion components. (Say, F/B representing Forward and Backward, and L/R representing Left or Right.) These electrical signals F/B and L/R are coupled to the computer, where software responds to the signals to change by a .DELTA.x and a .DELTA.y the displayed position of a pointer (cursor) in accordance with movement of the mouse. The user moves the mouse as necessary to get the displayed pointer into a desired location or position. Once the pointer on the screen points at an object or location of interest, one of one or more buttons on the mouse is activated with the fingers of the hand holding the mouse. The activation serves as an instruction to take some action, the nature of which is defined by the software in the computer.
Unfortunately, the usual sort of mouse described above is subject to a number of shortcomings. Among these are deterioration of the mouse ball or damage to its surface, deterioration or damage to the surface of the mouse pad, and degradation of the ease of rotation for the contact rollers (say, (a) owing to the accumulation of dirt or of lint, or (b) because of wear, or (c) both (a) and (b)). All of these things can contribute to erratic or total failure of the mouse to perform as needed. These episodes can be rather frustrating for the user, whose complaint might be that while the cursor on the screen moves in all other directions, he can't get the cursor to, say, move downwards. Accordingly, industry has responded by making the mouse ball removable for easy replacement and for the cleaning of the recessed region into which it fits. Enhanced mouse ball hygiene was also a prime motivation in the introduction of mouse pads. Nevertheless, some users become extremely disgusted with their particular mouse of the moment when these remedies appear to be of no avail. Mouse and mouse pad replacement is a lively business.
The underlying reason for all this trouble is that the conventional mouse is largely mechanical in its construction and operation, and relies to a significant degree on a fairly delicate compromise about how mechanical forces are developed and transferred.
There have been several earlier attempts to use optical methods as replacements for mechanical ones. These have included the use of photo detectors to respond to mouse motion over specially marked mouse pads, and to respond to the motion of a specially striped mouse ball. U.S. Pat. No. 4,799,055 describes an optical mouse that does not require any specially pre-marked surface. (Its disclosed two orthogonal one pixel wide linear arrays of photo sensors in the X and Y directions and its state-machine motion detection mechanism make it a distant early cousin to the technique of the incorporated Patents, although it is our view that the shifted and correlated array [pixel pattern within an area] technique of the incorporated Patents is considerably more sophisticated and robust.) To date, and despite decades of user frustration with the mechanical mouse, none of these earlier optical techniques has been widely accepted as a satisfactory replacement for the conventional mechanical mouse. Thus, it would be desirable if there were a non-mechanical mouse that is viable from a manufacturing perspective, relatively inexpensive, reliable, and that appears to the user as essentially the operational equivalent of the conventional mouse. This need could be met by a new type of optical mouse has a familiar "feel" and is free of unexpected behaviors. It would be even better if the operation of this new optical mouse did not rely upon cooperation with a mouse pad, whether special or otherwise, but was instead able to navigate upon almost any arbitrary surface.